1. 4.2 Niches and Community Interactions
Lesson Overview
4.2 Niches and Community Interactions

2. The Niche
What is a niche?
A _________is the range of physical and biological conditions in which a species lives and the way the species obtains what it needs to survive and reproduce.

3. Tolerance
Every species has its own range of ___________, the ability to survive and reproduce under a range of environmental circumstances.

4. Tolerance
When an environmental condition, such as _______________, extends in either direction beyond an organism’s optimum range, the organism experiences ____________________.
The organism must expend more energy to _______________ ________________, and so has less energy left for growth and reproduction.

5. Tolerance
Organisms have an _________________of tolerance for every environmental factor. Beyond those limits, the organism cannot survive.
A species’ tolerance for environmental conditions, then, helps determine its ____________—the general place where an organism lives.

6. Defining the Niche
An organism’s ___________ describes not only the environment where it lives, but how it interacts with biotic and abiotic factors in the environment.
In other words, an organism’s niche includes not only the _________and ______________ aspects of its environment, but also the way in which the organism uses them to survive and reproduce.

7. Resources and the Niche
The term ________________can refer to any necessity of life, such as water, nutrients, light, food, or space.
For plants, resources can include _________ ____________________________________.
For animals, resources can include ________ ____________________________________

8. Physical Aspects of the Niche
Part of an organism’s niche involves the ________________ it requires for survival.
Most amphibians, for example, lose and absorb water through their skin, so they must live in ___________________.
If an area is too hot and dry, or too cold for too long, most amphibians cannot survive.

9. Biological Aspects of the Niche
Biological aspects of an organism’s niche involve the _________________ it requires for survival, such as when and how it reproduces, the food it eats, and the way in which it obtains that food.
Birds on Christmas Island in the Indian Ocean, for example, all live in the same habitat but they prey on fish of different sizes and feed in different places.
Thus, each species occupies a distinct ___________.

10. How does competition shape communities?
By causing species to divide resources, ________________ helps determine the number and kinds of species in a community and the niche each species occupies.

11. Competition
How one organism ____________ ____________is an important part of defining its niche.
___________________ occurs when organisms attempt to use the same limited ecological resource in the same place at the same time.

12. Competition
In a forest, for example, plant roots compete for resources such as _________________ in the soil.
Animals ___________ for resources such as food, mates, and places to live and raise their young.
Competition can occur both between members of the _______________(known as ____________ _____________) and between members of _____________________ (known as _________ _________________________).

13. The Competitive Exclusion Principle
____________________ between different species almost always produces a winner and a loser—and the losing species dies out.

14. The Competitive Exclusion Principle
In the the experiment shown in the graph, two species of paramecia (P. aurelia and P. caudatum) were first grown in separate cultures (dashed lines) . In separate cultures, but under the same conditions, both populations grew.
However, when both species were grown together in the same culture (solid line), one species ___________________ the other, and the less competitive species ___________________.

15. The Competitive Exclusion Principle
The ______________________________ states that no two species can occupy exactly the same niche in exactly the same habitat at exactly the same time.
If two species attempt to occupy the same niche, one species will be better at competing for limited resources and will eventually exclude the other species.
As a result of competitive exclusion, natural communities rarely have niches that____________ ___________________.

16. Dividing Resources
Instead of competing for similar resources, species usually__________________.
For example, the three species of North American warblers shown all live in the same trees and feed on insects.
But one species feeds on high branches; another feeds on low branches, and another feeds in the middle.

17. Dividing Resources
The resources utilized by these species are similar yet different. Therefore, each species has its _____________________ and competition is minimized.
This division of resources was likely brought about by _____ ____________among the birds.
By causing species to divide resources, ____________helps determine the number and kinds of species in a community and the niche each species occupies

18. Predation, Herbivory, and Keystone Species
How do predation and herbivory shape communities?
_____________________ can affect the size of prey populations in a community and determine the places prey can live and feed.
_____________________ can affect both the size and distribution of plant populations in a community and determine the places that certain plants can survive and grow.

19. Predator-Prey Relationships
An interaction in which one animal (the predator) captures and feeds on another animal (the prey) is called___________________.
________________ can affect the size of prey populations in a community and determine the places prey can live and feed.
_____________, for example, can play an important role in regulating the population sizes of mice, voles, and other small mammals.

20. Predator-Prey Relationships
This graph shows an idealized computer model of changes in predator and prey populations over time.

21. Herbivore-Plant Relationships
An interaction in which one animal (the herbivore) feeds on producers (such as plants) is called ____________________.
__________________, like a ring-tailed lemur, can affect both the size and distribution of plant populations in a community and determine the places that certain plants can survive and grow.
For example, very dense populations of _______ ______________are eliminating their favorite food plants from many places across the United States.

22. Keystone Species
Sometimes changes in the population of a single species, often called a___________________, can cause dramatic changes in the structure of a community.
In the cold waters off the Pacific coast of North America, for example, ______________ devour large quantities of _________________.
Urchins are herbivores whose favorite food is_____, giant algae that grow in undersea “forests.”

23. Keystone Species
A century ago, sea otters were nearly eliminated by hunting. Unexpectedly, the kelp forest nearly vanished.
Without otters as predators, the sea urchin population skyrocketed, and armies of urchins devoured kelp down to bare rock.
Without kelp to provide habitat, many other animals, including seabirds, disappeared.
Otters were a ______________ in this community.

24. Keystone Species
After otters were protected as an endangered species, their population began to recover.
As otters returned, the urchin populations dropped, and kelp forests began to thrive again.
Recently, however, the otter population has been falling again, and no one knows why.

25. Symbioses
What are the three primary ways that organisms depend on each other?
Biologists recognize three main classes of symbiotic relationships in nature:
______________________

26. Symbioses
Any relationship in which two species live closely together is called ______________ , which means “living together.”

27. Mutualism
The ____________________ sting has two functions: to capture prey and to protect the anemone from predators. Even so, certain fish manage to snack on anemone tentacles.
The_____________, however, is immune to anemone stings. When threatened by a predator, clownfish seek shelter by snuggling deep into an anemone’s tentacles.

28. Mutualism
If an anemone-eating species tries to attack the anemone, the clownfish dart out and chase away the predators.
This kind of relationship between species in which both benefit is known as ____________________.

29. Parasitism
________________live in the intestines of mammals, where they absorb large amounts of their hosts’ food.
____________________ shown, live on the bodies of mammals and feed on their blood and skin.
These are examples of ______________________, relationships in which one organism lives inside or on another organism and harms it.

30. Parasitism
The ______________ obtains all or part of its nutritional needs from the host organism.
Generally, parasites___________ ____________________, which is usually larger than the parasite.

31. Commensalism
________________ often attach themselves to a whale’s skin. They perform no known service to the whale, nor do they harm it. Yet the ________________ from the constant movement of water—that is full of food particles—past the swimming whale.
This is an example of __________________, a relationship in which one organism benefits and the other is neither helped nor harmed.